Artificial intraocular lenses are widely used to replace the human crystalline lens of the eye. The human crystalline lens is a living transparent structure composed primarily of protein having a thickness of about five millimeters and a diameter of about nine millimeters. The lens is suspended behind the iris by zonula fibers that connect the lens to the ciliary body. A lens capsule surrounds the lens; the front portion of the capsule generally referred to as the anterior capsule and the back portion generally referred to as the posterior capsule.
The term "cataract" refers to the opacity of the lens of the eye. There are a variety of types of cataracts and for most cataracts, surgical intervention is required to remove and replace the lens with an artificial intraocular lens.
The transparency of the lens depends on the physiochemical state of the lens proteins. These proteins, like the proteins of other organs, are sensitive to changes in the properties of their surrounding fluid. Changes in the concentration of dissolved salts, in the osmotic pressure, in the pH or in the enzyme activity of the surrounding fluid can alter the properties of the lens proteins. Also, like other organs, changes to the proteins of the lens occur with age. A common type of cataract that occurs in elderly people is known as a senile cataract. This type of cataract has no known etiology and none of the forms of cataract produced experimentally to date closely resemble the senile cataract.
Artificial intraocular lenses generally comprise an optical region and a support, or haptic, to facilitate positioning and centering of the intraocular lens within the eye. Intraocular lenses have been made from a number of different materials. For example, hard lenses have been prepared from polymethylnethacrylate (PMMA) and optical glass while flexible lenses have been prepared from silicone, polyHEMA (polyhydroxyethylmethymethacrylate), acrylics, collagen, and combinations thereof. Flexible lenses have the advantage that they can be folded or otherwise deformed prior to implantation to reduce the overall size of the lens during the artificial lens implantation procedure.
There are a number of procedures and devices that have been developed for the removal of the natural lens followed by the insertion of an artificial lens. The extraction procedure can generally be categorized as intracapsular (i.e., where the lens is removed together with the lens capsule) or extracapsular (such as where a portion of the anterior capsule is circularly removed (capsulorhexis) and the posterior capsule is left intact).
Presently, phacoemulsification is a widely used method for the removal of diseased or damaged natural lens tissue. The phacoemulsification process generally employs a small incision typically of about 2 millimeters (mm) to about 4 mm in length (but potentially as small as 1 mm) through the cornea and a probe is used to ultrasonically break apart and remove the crystalline lens through the capsulorhexis.
There are a number of intraocular lens injectors that have been described in the literature to position a deformable artificial intraocular lens in the eye. These injectors use an incision of about 2 mm to about 4 mm, the incision size most frequently used in most phacoemulsification procedures. A larger (about 4 mm to about 5 mm) capsulorhexis incision, also used in phacoemulsification procedures, is used to position the lens without requiring elongation of the incision during the injection process.
U.S. Pat. No. 4,681,102 to Bartell discloses one type of device to implant an intraocular lens through a small incision. The injector comprises a load chamber that is used to fold a soft intraocular lens into a shape having a smaller cross-sectional area than the original unfolded cross-sectional dimension of the lens. The load chamber comprises two hinged members that together define a generally cylindrical lumen. Each of the two members includes a flange that extends non-parallel to cylindrical members at a point of connection and permits manipulation of the cylindrical members from a first open position to a second closed position. The intraocular lens is inserted into the load chamber when the two members are in an open position. The flanges are advanced towards each other causing the two members to form the generally cylindrical chamber. As the two members advance towards each other, the intraocular lens that is inserted in the chamber is compressed to conform to the generally cylindrical shape of the members in the closed position. This device and those devices that include a rigid chamber for deforming the lens can damage the lens during the deformation process if the lens is not accurately and carefully positioned in the chamber.
A number of patents use a pushrod (also described in these patents as a pusher or piston-type device) to apply a force directly on a lens and to push the deformed lens from the device into the eye. For example, the loading chamber of Bartell (supra) is placed into a rigid injector portion fitted with a pushrod. The pushrod pushes the intraocular lens through a generally circular lumen of the loading chamber and into an injector nozzle. The pushing action of the pushrod can further damage the lens material and haptics before the lens is positioned in the eye.
U.S. Pat. Nos. 4,702,244 and 4,573,998 to Mazzocco discloses a pushrod type of device that functions similar to a plunger of a syringe to provide a hydraulic force on a lens. The device includes a chamber for containing the intraocular lens in an unstressed state and for orienting the lens in a prescribed orientation to facilitate lens placement within the eye. The plunger is used to exert a direct force on the lens or a direct force on liquid surrounding the lens, sufficient to deform the lens such that the optical zone is deformed to a substantially smaller cross-sectional diameter than the optical zone in an unstressed state. The device includes a means to expel the lens from the device for placement in the eye. The surgical device disclosed by Mazzocco requires the use of a direct force such as a hydraulic force or a pneumatic force to move the lens from its unstressed stated into a deformed position. In the embodiment that compresses the lens from an unstressed state to a stressed state, the lens is propelled toward a small opening at the end of a holding tube. As the lens approaches the opening it is folded back against itself and compressed to fit through the opening. The orientation of the lens in the device is not uniform, nor would deformation be consistent with each injection. Moreover, the hydraulic force would likely be quite high and this pressure is likely not practical for use in the internal aspects of the eye.
U.S. Pat. No. 5,468,246 to Blake discloses another type of intraocular lens injector that compresses the diameter of the intraocular lens by rolling the lens into a tight cylindrical tube that can be inserted into the eye through a small incision of about 2 millimeters to about 4 millimeters. This device also uses a pushrod-type device to apply a direct force to move the lens from the injector device into the eye.
U.S. Pat. No. 5,562,676 to Brady, U.S. Pat. No. 5,275,604 to Rheinish, U.S. Pat. No. 5,474,562 to Orchowski, U.S. Pat. No. 4,919,150 to Stoy, U.S. Pat. No. 5,123,905 to Kelman and U.S. Pat. No. 5,616,148 to Eagles use an injector with a tapered or conical loading chamber to guide and fold the lens into a rigid lumen. These patents also use a pushrod to inject the lens from the lumen into the eye. A problem with these injectors is that the internally positioned pushrod is in direct contact with the lens assembly. This direct contact can result in distortion, bending or breakage of a trailing haptic. In addition, compressive forces on soft or fragile lens materials can tear the lens or destroy a haptic. In addition, during compression, the pushrod can catch or wedge a portion of the lens between the rigid lumen of the device and the pushrod mechanism.
There remains a need for a device for introducing a flexible implant, particularly fragile foldable lenses into the body without damaging that implant. In particular, there is a need for a device to implant a foldable intraocular lens into an eye without damaging the lens or the haptics during the implantation process.